Search results for "electrostatic"
showing 10 items of 134 documents
α-d-Glucopyranose Adsorption on a Pd30 Cluster Supported on Boron Nitride Nanotube
2016
Boron nitride nanotube (BNNT) as an innovative support for carbohydrate transformation processes was evaluated, using density functional theory. The α-d-glucopyranose adsorption on a Pd30 cluster, supported on BNNT, was used to check both the local activity of topologically different metallic sites and the effects of the proximity of the BNNT surface to the same metallic sites. Detailed geometrical and electronic analyses performed on Pd30/BNNT and α-d-glucopyranose/Pd30/BNNT systems were discussed. It was observed that the deposition of the Pd30 cluster onto the BNNT support gives rise to an electronic rearrangement, determining a charge transfer from the support to the adsorbed metal clus…
IR fingerprints of U(VI) nitrate monoamides complexes: a joint experimental and theoretical study.
2010
Infrared spectra of 0.5 mol·L-1 uranium(VI) nitrate monoamide complexes in toluene have been recorded and compared with infrared spectra calculated by DFT. The investigated monoamides were N,N- dimethylformamide (DMF), N,N-dibutylformamide (DBF), and N,N- dicyclohexylformamide (DcHF). The validity of DFT calculations for describing uranium nitrate monoamide complexes has been confirmed as a fair agreement between experimental and calculated spectra was obtained. Furthermore, a topological analysis of the electron density has been carried out to characterize monoamide-uranium interactions. From this work, it appears that the increase of stability of uranylmonoamide complexes may be directly …
Generic nature of long-range repulsion mechanism on a bulk insulator?
2017
Dynamic atomic force microscopy measurements are reported that provide evidence for the presence of long-range repulsion in molecular self-assembly on a bulk insulator surface. We present the structures formed from four different benzoic acid derivatives on the (10.4) cleavage plane of calcite kept in ultra-high vacuum. These molecules have in common that they self-assemble into molecular stripes when deposited onto the surface held at room temperature. For all molecules tested, a detailed analysis of the stripe-to-stripe distance distribution reveals a clear deviation from what would be expected for randomly placed, non-interacting stripes (i.e., geometric distribution). When excluding kin…
N ‐Annulated Perylene Bisimides to Bias the Differentiation of Metastable Supramolecular Assemblies into J‐ and H‐Aggregates
2020
The unique self-assembling features of N-annulated perylene bisimides (PBIs) 1 and 2 are reported. The stability of the aggregates of diester 1, in which no H-bonding interactions are operative, corroborates the significance of long-range van der Waals and dipole-dipole electrostatic interactions in the construction of stable supramolecular assemblies. The incorporation of amide functional groups within the N-annulated PBI in 2 stimulates pathway differentiation to achieve up to three J-type aggregates and a fourth H-type aggregate depending on the experimental conditions. The results presented demonstrate unprecedented levels of control over synthetic supramolecular self-assembly and the r…
Solution properties of polyelectrolytes
1993
Abstract Aqueous size-exclusion chromatography was used to analyse the elution behaviour of several standard ionic polymers, including poly( l -glutamic acid), sodium poly(styrene sulphonate) and poly(acrylic acid), different in nature and chain flexibility, as a function of the pH and ionic strength of the eluent. Two organic-based hydrophilic packings, Spherogel TSK PW4000 and Ultrahydrogel 250, were tested in order to select the optimal conditions of macromolecular separation, and the results obtained for each column were compared. A set of calibration graphs for the above polyions as a function of eluent pH and ionic strength were obtained and compared with those obtained for uncharged …
Solution properties of polyelectrolytes XII. Semi-quantitative approach to mixed electrostatic and hydrophobic polymer-gel interactions
1996
Abstract Aqueous size-exclusion chromatography of polyanions, where secondary effects affect the total separation mechanism, was investigated. For elution of polyelectrolytes on inorganic silica-based supports, the electrostatic polymer-gel repulsive interactions were evaluated through the values for a hypothetical repulsion layer, X e , according to the model developed by other workers. Using a similar procedure, the existence of an effective barrier defined as X e − X h is proposed for those systems in which electrostatic repulsion and hydrophobic interactions take place simultaneously as secondary mechanisms. X h can be viewed as a measure of the “enlargement” of the geometrical pore rad…
Ionic transport characteristics of negatively and positively charged conical nanopores in 1:1, 2:1, 3:1, 2:2, 1:2, and 1:3 electrolytes
2019
We study experimentally the current (I)-voltage (V) curves of 1:1, 2:1, 3:1, 2:2, 1:2, and 1:3 electrolytes in positively and negatively charged conically-shaped pores of nanoscale dimensions. The positive charges are poly(allylamine hydrochloride) chains functionalized on the pore surface by electrostatic interactions while the negative charges are carboxylic acid groups. Under physiological conditions, these fixed-charge groups are ionized and strongly interact with the different monovalent, divalent, and trivalent ions in the pore solution. The current rectification of the I-V curves and the membrane potentials provide fundamental information on the interaction of the pore charge groups …
Protein Flexibility and Preorganization in the Design of Enzymes. The Kemp Elimination Catalyzed by HG3.17
2015
A recently designed enzyme, HG3.17, obtained by directed evolution, has shown a catalytic activity close to natural enzymes. Hybrid QM/MM molecular dynamics simulations for the Kemp elimination in this new enzyme have provided a deep insight into the origin of its catalytic efficiency. In this case, we have first demonstrated the presence of different conformations with significantly different reactivity. The larger reactivity is related with a better electrostatic preorganization of the environment that creates a more favorable electrostatic potential for the reaction to proceed. In HG3.17, efforts to improve the catalytic properties must be focused in possible mutations increasing the pre…
Equilibrium and transport properties of ion-exchange membranes
1984
Abstract Specific properties (ion-exchange capacity, water content, pore volume fraction) and transport properties (counterion transport number and electrical conductivity) have been measured in four commercial cation-exchange membranes loaded with a variety of cations of different nature and charge. Not surprisingly, equivalent conductances are lower than in free solution and transport numbers decrease with valency of the counterion. This behavior is explained by taking into account a “tortuosity factor”, due to a lengthening of the pores across the membrane, except for a membrane with a lower water content and for ions of higher charge, in which electrostatic interactions between mobile a…
Highly Defined, Colloid‐Like Ionic Clusters in Solution
2012
Many societal challenges at the beginning of the 21st century lead to an apparent and growing need for functional materials and novel ways of materials synthesis and assembly. Rising to the challenge, the utilization of small, self-assembling building blocks for the bottom-up construction of new types of polymers and nanostructures has enjoyed increasing popularity among materials researchers in the recent past. Supramolecular materials like foldamers, surface films, nanoparticles, etc. are created by exploiting noncovalent forces [1] leading to an ordered arrangement of nanoscale building blocks. [2] In the search for new polymers based on noncovalent molecular forces, we are motivated by …